Optical systems are now commonly used in place of magnetic systems for recording and retrieval of digitized information. In optical recorders, the data is used to digitally modulate a light beam having a predetermined intensity necessary to mark a light sensitive recording media. The modulated beam is focused to a small spot and traced across the media to record the data as a fine optical pattern comprised of a number of closely spaced, microscopic dots (data marks) along a data track. A data track may contain a plurality of data channels depending on the number of write beams. To recover the recorded data from the optical media, a low intensity illumination beam is scanned along the data track and modulated by the optical pattern recorded therein. The modulated beam is reflected from the media to illuminate a light detector producing an electrical signal in accordance with the beam modulation for recovery of the recorded data.
Increased delta rates require retrieval (or recordal) of multiple data channels simultaneously and/or increased scanning velocities. Difficulties arise when attempting to achieve both effectively in a compact opto-mechanical volume. While a single beam device may be provided in a compact volume, higher data rates require additional laser power and complex, high velocity scanners. Such systems include rotational scanners in disk systems, transverse scanners in certain lens systems, transverse linear air bearing scanners land acousto-optic scanners. The problem with such scanning systems is the cost and complexity in the scanning optics and mechanics.
Use of multiple write beams can reduce the need for complex scanning optics and mechanics. However, the disadvantage of present multiple write beam architecture is that it increases the volume (size) of the write head. At least two alternatives exist for introducing multiple write beams. One way is to use a number of discrete collimated laser diodes and spatially combine the outputs for focusing on the recording media by a final objective lens. The separation between each data channel is dictated by the angles of the beams as they enter the final objective lens, Since the objective lens has a limited field of view, the smaller the angles, the more compact the write head can be constructed. Smaller angles can be achieved through intervening optics to reduce the incoming angles, thus decreasing the separation between data channels (and increasing data density). However, this produces a system that is more complex and costly.
Another way is to use a single high-powered laser diode and a spatial light modulator to provide multiple distinct data beams. The problems with this type of system include laser power requirements (the number of parallel data channels is limited by both the field of view of the objective lens and the available laser diode power), channel intensity variations due to spatially sampling different portions of a laser beam with a Gaussian profile and increase complexity introduced by the spatial light modulator.
Accordingly, there is a need for a system incorporating multiple write beams to increase the aggregate data rate without significantly increasing the size of the write head and without complex scanning optics and mechanisms (e.g. lens wheel, linear air bearing, acousto-optic scanner). A system is needed that can reduce or eliminate external modulation requirements (spatial light modulator) and precision optomechanics required for diode-to-diode pointing. Furthermore, in longitudinal systems (data recorded longitudinally on the optical tape) where the write pulse length is sufficiently long such that thermal effects at the recording media between adjacent data channels affect the recorded data mark size, it is advantageous to maximize the spatial distance between two adjacent focused data mark spots to minimize thermal adjacency effects while still providing short separation of the data channels. Additionally, a system is needed having a write head that is simple, compact and low in cost.